Maybe your high school gym coach had you do sit-ups during gym class, and you did what you were told to avoid getting detention or being sent to the principal’s office. The truth is, you should have told your coach, “Wait a minute, bub— doing sit-ups might overload the abs, but they also cause back injury.” That’s what the scientific research shows— traditional sit-ups (straight-leg or bent knee) place heavy and potentially harmful loads on your spinal disks. Do enough sit-ups and you will probably suffer a back injury. Instead, do curl-ups— the “back friendly” way to a ripped midsection and a killer six-pack.
Work Your Core, Not Just Your Abs
To train your abs without hurting your back, look at the big picture and strengthen your core along with your abs. The core is a corset of muscles and connective tissue that surrounds and holds the spine in place. The muscles forming the core must be balanced to allow the spine to support heavy loads. If you focus on working only one set of muscles in the core, you can destabilize your spine by pulling it out of alignment. The solution is a core-training program that works all major muscles that girdle the spine, including the abs.
Curl-ups are one of three important exercises that will strengthen your core muscles and help build and define your abs. They develop the rectus abdominis muscle, or front of the abdomen. Other ab essentials are side-bridges (aka side planks) that work the obliques (sides of the abdomen) and the quadratus lumborum muscle, a deep muscle that helps stabilize the spine. Bird-dog exercises build the spinal extensor muscles, which are embedded in the back and sides of the core. Electromyography (EMG) studies show that these exercises best load their respective target muscles while minimizing the load on the spine, so they should be part of your ab training.
Feeding Your Abs
Unless you incorporate a healthy nutritional program and regular cardiovascular exercise to keep body fat low, you can do curl-ups until you’re unconscious (or worse) and you still won’t have a rock-hard midsection. To really see your abs and showcase the fruits of your labor in the gym, eat a low-glycemic diet that’s high in protein and lower in carbs like the Mediterranean diet. Avoid refined sugars and starches like bread and pasta; many nutritionists advise against consuming dairy and fruit, for that matter. Consult a registered dietitian or ask your doctor for guidance.
Staying lean has benefits beyond being able to see your abs. Having a large waist size is an early warning sign for diabetes. While obesity is a clear-cut risk factor for diabetes, doctors have a harder time determining which overweight people might be at risk for diabetes. “Waist circumference is very helpful in people who are obese, but exceptionally helpful in people who are overweight,” Dr. Abraham Thomas, M.D., head of endocrinology and diabetes at Henry Ford Hospital in Detroit, told CNN. So eating healthfully, staying lean and exercising will give you more than great abs. It will keep you out of the diabetes zone.
The take-home message is you don’t get a six-pack by eating cookies and doughnuts. When you go into Starbucks for coffee in the morning and eye that multigrain bagel in the counter, tell yourself: “You want a flabby midsection and a fat butt? Then go for the bagel.”
Timing Is Everything
While doing curl-ups, be quick about it. Don’t do your exercises like you’re in a coma. Research shows that fast curl-ups recruit the most muscle fibers. While slow, controlled contractions activate the muscle fibers best during many weight-training exercises, that’s not the case for curl-ups.
In a study published in the Journal Strength Conditioning Research, Spanish researchers measured abdominal muscle activation levels during fast and slow curl-ups by electromyography (EMG). They attached electrodes to the rectus abdominis (six-pack muscle), internal and external obliques (side abs) and the erector spinae (spinal) muscles. The researchers measured muscle activity while the subjects did curl-ups at four different speeds ranging from 1 rep per four seconds to maximum-speed curl-ups. Activation levels increased in each muscle as speed increased. Researchers concluded that doing curl-ups at fast speeds was best for overloading the abdominal muscles and building dynamic spinal stability.
Faster ab training is better, but don’t do the exercise so fast that you can’t maintain good technique.
Doing curl-ups with your feet on a bench as opposed to the floor is a more back-friendly version that will enable you to focus more on working your ab muscles, and takes stress away from your hip flexors.
1. Lie on your back on a mat. Keep one knee bent with your hands positioned under your lower back for support. Place your other foot on the bench.
2. Curl up to slowly and gently lift your head and shoulders slightly off the floor, without bending your lower back and spine. Keeping your shoulders off the floor prevents prying the upper body through the shoulders. The center of rotation should be at the mid-back (thoracic vertebrae) to avoid excessive neck movement (cervical flexion).
3. Do not allow your stomach to become indented or sunken, and don’t press your back against the floor.
4. Once you are in the correct position, hold it for 8-10 seconds. This counts for 1 repetition.
5. Repeat as many times as possible in five minutes.
Keep in Mind
• Curl-ups progress by first pre-activating the rectus abdominis and then the obliques (which act as the brace), so the challenge involves increased curling against the brace— not with more flexion.
• Breathe deeply while you maintain a stable spine.
• Never curl up as far as possible because it places too much bending stress on your spinal disks.
• Consult a certified personal trainer if you are unsure about proper form and technique. This exercise can be modified to suit your fitness level.
Swiss Ball Curl-Ups
Take your ab training to the next level by doing curl-ups on a Swiss or stability ball. Not only will working on the stability ball improve your balance and introduce a new challenge to your workout, but it will also torch your abs.
In research published in the Journal of Strength and Conditioning Research, EMG studies were used to measure abdominal muscle activity of subjects doing traditional crunches versus subjects doing curl-ups on a stability ball. Using a stability ball “significantly increased muscle activity” in the lower and upper portions of the rectus abdominis and external oblique muscles when subjects performed curl-ups, but placement of the ball is vital. Muscle activity doubled when the ball was placed at the level of the lower lumbar region of the back, compared to placing the ball higher at the level of the inferior angles of the scapula.
So if you do your curl-ups on a stability ball, you’ve got to lowball it. Here’s how:
1. Lie on your back on the Swiss ball. Start with your thighs and torso parallel with the floor. Your entire back and shoulders (but not your head) should be on the ball, and your butt should be just off the ball. You want your lower back to be supported by the ball when you curl up.
2. Cross your arms over your chest and touch each hand to the opposite shoulder. Pull your belly button into your spine and keep your abs tight at all times. Contract your rectus abdominis, slowly raising your torso no more than 45 degrees— just short of an upright position. Slowly lower yourself to the starting position.
3. Increase the stress on your oblique muscles by moving your feet closer together. Focus on working the rectus abdominis rather than the shoulder and neck muscles.
Axler CT and McGill SM. Low back loads over a variety of abdominal exercises: searching for the safest abdominal challenge. Med Sci Sports Exerc 1997;29:804-811.
Waist size signals diabetes risk
Cordo PJ, Gurfinkel VS, et al. The sit-up: complex kinematics and muscle activity in voluntary axial movement. J Electromyogr Kinesiol 2003;13: 239-252.
Fahey T. Basic Weight Training for Men and Women. New York: McGraw Hill, 2004. (5th edition).
Fahey T. Fit and Well. New York: McGraw Hill, 2003 (5th edition).
Green JP, Grenier SG, et al. Low-back stiffness is altered with warm-up and bench rest: implications for athletes. Med Sci Sports Exerc 2002;34:1076-1081.
McGill SM. Low back exercises: evidence for improving exercise regimens. Phys Ther 1998;78: 754-765.
McGill, SM. Low Back Disorders. Champaign, IL: Human Kinetics, 2002. Medical College of Georgia. Research pinpoints variations in sit-up techniques. Press release, Aug. 15, 2003.
Shrier I, Feldman D, et al. Comparison between tests of fatigue and force for trunk flexion. Spine 2003; 28: 1373-1378, 2003.
Suzuki J, Tanaka R, et al. Assessment of abdominal muscle contractility, strength, and fatigue. Am J Respir Crit Care Med 1999;159:1052-1060.
Vera-Garcia FJ, Grenier SG, et al. Abdominal muscle response during curl-ups on both stable and labile surfaces. Phys Ther 2000;80:564-569.
Journal of Strength and Conditioning Research 2007;21(2):506-509.